Nothing can be learned overnight. Only by working patiently, you can reach the goal: succeed in sight reading as if reading an ordinary, literal text. It is therefore essential that you practice 10 minutes a day and improve the technique of sight reading.
Begin, for example, with the etudes for I and II class of some until then unknown school to you .
First look at the note text (score), analyze tonality (key signature), the type of bar (time signature), technical problems, etc. and set the speed (tempo), in which you will play. If you make a mistake while playing, do not go back to correct it, but continue playing until the end. After that, go back to where you have made mistakes, analyze them and play the entire etude at the same speed. Then play for the third time, but now at a slightly faster speed at which you can control all the elements of good playing. Play the other etudes in the same way – and in your 10-minute daily practice of sight reading.
Subsequently, sight reading will be very useful to you for each note text (score) that gets in your hands. You will notice that no longer any new note text (sight reading of new composition) can surprise you.
Taken from my book